Parallel hybrid drive trains, known from the practice, are designed with at least one electric engine and one output. For starting the internal combustion engine, the electric engine is situated in the power train between the output and the internal combustion engine. One frictionally engaged shifting element is respectively provided between the internal combustion engine and the electric engine and also between the electric engine and the output so that the vehicle can be operated, in different operating states, by the internal combustion engine or the electric engine. The output torque, abutting on the output of the parallel hybrid drive train, is essentially dependent on the torque produced by the electric motor and/or the internal combustion engine as well as being dependent on the transmitting capacities adjusted in the area of the shifting elements.
It is possible, for example, to disengage the internal combustion engine from the power flow of the drive train by opening the shifting element provided between the internal combustion engine and the electric engine and to drive the vehicle with adequate output torque, via a purely electromotive drive.
By placing a shifting element between the electric engine and the internal combustion engine, it is further possible to couple the disengaged internal combustion engine to the power flow of the drive train in almost all operating states of the drive train without generating reaction torques on the output that impair the riding comfort. This is attainable by adequate control and regulation of the transmitting capacity of the added shifting element, situated between the electric engine and the output.
In addition to starting the internal combustion engine, it is also possible, via an adequate slip operation of the shifting element situated between the electric engine and the internal combustion engine, to synchronize the internal combustion engine with the remaining part of a parallel hybrid drive train and couple it thereto free of reaction torques.
In addition to a vehicle designed with a parallel hybrid drive train, the conventional vehicles built with only one internal combustion engine, starting is possible only by way of the internal combustion engine. At least the shifting element located between the internal combustion engine and the electric engine or between the electric engine and the output, is slip operated and used as a starting element of the parallel hybrid drive train.
Alternative to this, it is also possible with a parallel hybrid drive train, during a starting process, to drive a vehicle simultaneously, via the electric engine and via the internal combustion engine, with at least one slipping shifting element. It is possible to convey in the direction of the output the input torque of the electric engine both in a slipping and in an engaged state of the shifting element between the electric engine and the output.
With a driving process joined together with the starting process of the vehicle, a parallel hybrid drive train can operate in a manner such that its output torque, preset by the driver, couples with the output of the vehicle and while driving, an energy accumulator of the vehicle, as a result of the electric engine acting as a generator, is unloaded or is loaded.
Moreover, an electric energy accumulator of the vehicle can be neutrally loaded while the electric engine is in a driving position by engaging the shifting element, located between the electric engine and the output; the same as by engaging the shifting element located between the electric engine and the internal combustion engine.
To be able to ensure increased riding comfort during the above described operation cycle, the input torques of the electric engine and the internal combustion engine to be adjusted depend on the operating state and/or the driver's desire, the same as the transmitting capacities to be adjusted in the range of the shifting elements depend on the operating state and/or on the driver's desire, have to be exactly coordinated with each other. Manufacture tolerances, determined by production, and by operation characteristics of the components, change over the service life of the components of the parallel hybrid drive train, on one hand, resulting in an operating characteristic differing from system to system. Operational characteristics of the components also change with the increasing duration of operation or service life of the components decreasing, resulting in an undesired diminishment of riding comfort.
Therefore, the problem on which this invention is based is to make a method available for operating a parallel hybrid drive train of a vehicle which, in the operation of a parallel hybrid drive train, the reduction of riding comfort is easily prevented.